Adding forces in a line
The observation from activity 1 can be written down as a rule.
Two collinear forces in the same direction
When two forces act collinearly in the same direction, the resultant of those two forces is equal to their sum.
resultant = force 1 + force 2
Direction: the same direction as the forces themselves.
Worked example 1
The problem
Two children pull, in the same direction, a string tied to a box resting on a table. One child applies a force of 8 N. The other applies 6 N. What is the resultant force with which the two children pull the box?
Solution
Both forces act in the same direction along the same string, so they add.
resultant force = 8 N + 6 N
resultant force = 14 N, in the direction the children are pulling.
Write the direction down
Do not stop at "14 N". For two forces in the same direction the resultant is in that same direction — and that is part of the answer, not an extra remark.